Devices for this same purpose exist in the market, in which when the band is unrolled, an internal spring is charged by torsion. When the band is released, the spring recovers and rotates a tube, on which the band rolls up.
Although perfectly valid, the construction of these devices is quite complex and the life of the spring relatively shortlived, working as it does through uncontrolled torsion.
The device of the present invention, preserving the outside appearance of existing devices, works by compression or, alternatively, traction of the spring.
This device is made up of a totally or partially threaded axis, the thread being divided longitudinally into equal and symmetric parts, although threaded in opposite directions.
On this axis two mobile circular pieces, resembling washers, are screwed, while a spring is inserted over the axis between those two circular pieces.
These mobile pieces have projections which fit into longitudinal grooves of an external tube, or inversely, they may have slits where longitudinal projections of the external tube fit.
The device is completed with lateral covers, with inserts of the diameter of the external tube cut out, on which the tube fits. In this way, the outside tube turns over these covers, which also serve as stoppers for the mobile pieces, when these reach their stop positions.
When the band is pulled to unroll it, the external tube causes the mobile pieces to rotate, traversing along the threads, compressing the spring, at the same time as they glide to the middle along the grooves/projections of the external tube.
When the band is released, the spring pushes the mobile pieces, which unscrew, forcing the external tube to rotate in the reverse direction, at the same time as they glide longitudinally along the grooves/projections until they reach the stoppers of the band or the spring is totally decompressed.
This device may also operate the other way around; i.e., instead of compressing the spring, it is pulled as the mobile pieces unscrew towards the ends of the axis. To operate this way, it is necessary that the spring is fastened to the mobile pieces, something which is not necessary when the device operates by compression.
The device can also be constructed with only one mobile piece, in which case the other end will push on the lateral cover, being fixed to the external tube and freely rotating around the axis (not screwed), needing therefore an additional cover piece as a stopper to avoid the displacement of the tube along the axis when rotating.
The device can be operated by manual or motorized means.
In order to complete the description and with the aim to help to better understand the characteristics of the invention, a set of drawings, based on the preferential practical realization of it, are included as integral part of this description. With illustrative and not limitative purpose, the following is shown: